Reforming wet-tantalum capacitors in implantable medical devices

ABSTRACT

Miniature defibrillators and cardioverters detect abnormal heart rhythms and automatically apply electrical therapy to restore normal heart function. Critical to this function, aluminum-electrolytic capacitors store and deliver life-saving bursts of electric charge to the heart. This type of capacitor requires regular “reform” to preserve its charging efficiency over time. Because reform expends valuable battery energy, manufacturers developed wet-tantalum capacitors, which are generally understood not to require reform. Yet, the present inventors discovered through extensive study that wet-tantalum capacitors exhibit progressively worse charging efficiency over time. Accordingly, to address this problem, the inventors devised unique reform techniques for wet-tantalum capacitors. One exemplary technique entails charging wet-tantalum capacitors to a voltage equal to about 90% of their rated voltage and allowing the charge to dissipate through system leakage for a period of time, before discharging through a non-therapeutic load.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/990,180, filed on Nov. 21, 2001, which iscontinuation-in-part of U.S. patent application Ser. No. 09/900,595filed on July, 6, 2001, which is a continuation of U.S. patentapplication Ser. No. 09/453,358 filed on Dec. 1, 1999, now issued asU.S. Pat. No. 6,283,985, the specifications of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention concerns capacitors used in medicaldevices, such as implantable defibrillators, cardioverters, pacemakers,and more particularly methods of maintaining capacitors in thesedevices.

[0003] Since the early 1980s, thousands of patients prone to irregularand sometimes life threatening heart rhythms have had miniaturedefibrillators and cardioverters implanted in their bodies. Thesedevices detect onset of abnormal heart rhythms and automatically applycorrective electrical therapy, specifically one or more bursts ofelectric current, to hearts. When the bursts of electric current areproperly sized and timed, they restore normal heart function withouthuman intervention, sparing patients considerable discomfort and oftensaving their lives.

[0004] The typical defibrillator or cardioverter includes a set ofelectrical leads, which extend from a sealed housing into the walls of aheart after implantation. Within the housing are a battery for supplyingpower, a capacitor for delivering bursts of electric current through theleads to the heart, and monitoring circuitry for monitoring the heartand determining when, where, and what electrical therapy to apply. Themonitoring circuitry generally includes a microprocessor and a memorythat stores instructions not only dictating how the microprocessoranswers therapy questions, but also controlling certain devicemaintenance functions, such as maintenance of the capacitors in thedevice.

[0005] The capacitors are typically aluminum electrolytic capacitors.This type of capacitor usually includes strips of aluminum foil andelectrolyte-impregnated paper. Each strip of aluminum foil is coveredwith an aluminum oxide which insulates the foils from the electrolyte inthe paper. One maintenance issue with aluminum electrolytic capacitorsconcerns the degradation of their charging efficiency after long periodsof inactivity. The degraded charging efficiency, which stems frominstability of the aluminum oxide in the liquid electrolyte, ultimatelyrequires the battery to progressively expend more and more energy tocharge the capacitors for providing therapy.

[0006] Thus, to repair this degradation, microprocessors are typicallyprogrammed to regularly charge and hold aluminum electrolytic capacitorsat or near a maximum-energy voltage (the voltage corresponding tomaximum energy) for a time period less than one minute, beforedischarging them internally through a non-therapeutic load. (In somecases, the maximum-energy voltage is allowed to leak off slowly ratherthan being maintained; in others, it is allowed to leak off (or droop)for 60 seconds and discharged through a non-therapeutic load; and instill other cases, the voltage is alternately held for five seconds anddrooped for 10 seconds over a total period of 30 seconds, before beingdischarged through a non-therapeutic load.) These periodiccharge-hold-discharge (or charge-hold-droop-discharge) cycles formaintenance are called “reforms.” Unfortunately, reforming aluminumelectrolytic capacitors tends to reduce battery life.

[0007] To eliminate the need to reform, manufacturers developedwet-tantalum capacitors. Wet-tantalum capacitors use tantalum andtantalum oxide instead of the aluminum and aluminum oxide of aluminumelectrolytic capacitors. Unlike aluminum oxide, tantalum oxide isreported to be stable in liquid electrolytes, and thus to require noenergy-consuming reforms. Moreover, conventional wisdom teaches thatholding wet-tantalum capacitors at high voltages, like those used inconventional reform procedures, decreases capacitor life. So, not onlyis reform thought unnecessary, it is also thought to be harmful towet-tantalum capacitors.

[0008] However, the present inventors discovered through extensive studythat wet-tantalum capacitors exhibit progressively worse chargingefficiency over time. Accordingly, there is a previously unidentifiedneed to preserve the charging efficiency of wet-tantalum capacitors.

SUMMARY OF THE INVENTION

[0009] To address this and other needs, the inventors devised methods ofmaintaining wet-tantalum capacitors in implantable medical devices. Oneexemplary method entails reforming this type of capacitor. Moreparticularly, the exemplary method entails charging wet-tantalumcapacitors to a high voltage and keeping the capacitors at a highvoltage for about five minutes, before discharging them through anon-therapeutic load. In contrast to conventional thinking, reformingwet-tantalum capacitors at least partially restores and preserves theircharging efficiency.

[0010] Another facet of the invention includes an implantable medicaldevice, such as defibrillator, cardioverter, cardioverter-defibrillator,or pacemaker, having one or more wet-tantalum or other type capacitorsand means for reforming the capacitors. Yet another facet includes acomputer-readable medium bearing instructions for reforming capacitorsaccording to one or more unique methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagram of an exemplary implantable heartmonitor incorporating teachings of the present invention.

[0012]FIG. 2 is a flow chart illustrating exemplary operation of theheart monitor of FIG. 1.

[0013]FIG. 3 is a state flow diagram illustrating an alternativeoperation of the heart monitor of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The following detailed description, which references andincorporates FIGS. 1-3, describes and illustrates one or more specificembodiments of the invention. These embodiments, offered not to limitbut only to exemplify and teach the invention, are shown and describedin sufficient detail to enable those skilled in the art to practice theinvention. Thus, where appropriate to avoid obscuring the invention, thedescription may omit certain information known to those of skill in theart.

[0015]FIG. 1 shows an exemplary implantable heart-monitoring device (orpulse generator) 100 incorporating teachings of the present invention.Device 100 includes a monitoring system 110, a lead system 120, atherapy system 130, a power system 140, and an interconnective bus 150.Monitoring system 110 includes a processor or microcontroller 112 and amemory 114. Memory 114 includes one or more software modules 116 whichstore one or more computer instructions in accord with the presentinvention. Some embodiments of the invention replace software modules116 with one or more hardware or firmware modules. In the exemplaryembodiment, processor 112 is similar to a ZiLOG™ Z80 microprocessor(with a math coprocessor), and memory 114 is a random-access memory.However, the invention is not limited to any particular microprocessor,microcontroller, or memory.

[0016] Lead system 120, in the exemplary embodiment, includes one ormore electrically conductive leads—for example, atrial, ventricular, ordefibrillation leads—suitable for insertion into a heart. One or more ofthese are suitable for sensing electrical signals from a portion of theheart and one or more are suitable for transmitting therapeutic doses ofelectrical energy. Lead system 120 also includes associated sensing andsignal-conditioning electronics, such as atrial or ventricular senseamplifiers and/or analog-to-digital converters, as known or will beknown in the art.

[0017] In some embodiments, lead system 120 supports ventricularepicardial rate sensing, atrial endocardial bipolar pacing and sensing,ventricular endocardial bipolar pacing and sensing, epicardial patches,and Endotak® Series and ancillary leads. In some embodiments, leadsystem 120 also supports two or more pacing regimens, including DDDpacing. Also, some embodiments use at least a portion of a housing ofdevice 100 as an optional defibrillation electrode. The invention,however, is not limited in terms of lead or electrode types, lead orelectrode configurations, pacing modes, sensing electronics, orsignal-conditioning electronics.

[0018] Therapy system 130 includes a capacitor system 132 and othercircuitry (not shown) for delivering or transmitting electrical energyin measured doses through lead system 120 to a heart or other livingtissue. Additionally, therapy system 130 includes one or more timers,analog-to-digital converters, and other conventional circuitry (notshown) for measuring various electrical properties related toperformance, use, and maintenance of the therapy system.

[0019] In the exemplary embodiment, capacitor system 132 include threeor four, flat or cylindrical wet-tantalum and/or other type capacitors.The exemplary wet-tantalum capacitors comprise a tantalum metal anode,Ta₂O₅ dielectric, a liquid electrolyte, and a cathode of material otherthan tantalum, for example, RuO₂. Capacitors of this description areknown in the trade as hybrid capacitors, with some versions havingtantalum cases and others having polypropylene cases. See also U.S. Pat.Nos. 5,982,609; 5,469,325; 5,737,181; and 5,754,394, which areincorporated herein by reference.

[0020] Exemplary specifications for the wet-tantalum capacitors are 185volts surge, 60 microamp leakage current at 175 volts, 90 microampleakage current at 185 volts, an AC capacitance of 490 microfarads, andequivalent series resistance (ESR) of 1.2 ohms. Capacitors meeting theseor specifications or having similar construction are manufactured byWilson Greatbatch Ltd. of Clarence, N.Y. or Evans Capacitor Company ofEast Providence, R.I.

[0021] In general operation, lead system 120 senses atrial orventricular electrical activity and provides data representative of thisactivity to monitoring system 110. Monitoring system 110, specificallyprocessor 112, processes this data according to instructions of softwaremodule 116 of memory 114. If appropriate, processor 112 then directs orcauses therapy system 130 to deliver one or more measured doses ofelectrical energy or other therapeutic agents through lead system 120 toa heart. Additionally, software module 116 includes one or moreinstructions or code segments which manage and maintain capacitors 132in accord with teachings of the inventions.

[0022]FIG. 2, which shows an exemplary flow chart 200, illustrates anexemplary capacitor-management method embodied within software module116 and executed by processor 112 and other relevant portions of device100. Flow chart 200 includes blocks 202-220, which are arranged seriallyin the exemplary embodiment. However, other embodiments of the inventionmay execute two or more blocks in parallel using multiple processors ora single processor organized as two or more virtual machines orsubprocessors. Moreover, still other embodiments implement the blocks astwo or more specific interconnected hardware modules with relatedcontrol and data signals communicated between and through the modules.Thus, the exemplary process flow applies to software, firmware, andhardware implementations.

[0023] In process block 202, processor 112 of device 100, determineswhether to initiate reform of the wet-tantalum capacitors. The exemplaryembodiment makes this determination based on whether a predeterminedamount of time, for example 30, 60, 90, or 120 days, has elapsed sincethe last reform or the last therapeutic use, that is, charge anddischarge, of the capacitor. Some embodiments use a timer to supportthis determination, with the timer in some embodiments being reset withevery therapeutic use or certain therapeutic uses of the capacitors andother embodiments ignoring therapeutic use of the capacitor as a factorinfluencing reform timing. Other embodiments trigger or schedule reformbased on thresholding of certain average or instantaneous performanceaspects of the capacitors, such as actual or estimated full-energycharge time. And still other embodiments initiate reform as part of anoverall storage mode. See also U.S. Pat. No. 5,899,923 which is entitledAutomatic Capacitor Maintenance System for an Implantable CardioverterDefibrillator and which is incorporated herein by reference.

[0024] If the processor determines that reform is presently undesirable,execution proceeds to block 206, where the reform procedure is aborted.In the exemplary embodiment, aborting the reform procedure entailsrescheduling it for some programmable amount of time in the future, forexample 23-25 hours later. However, if the processor determines thatreform is presently desirable, execution proceeds to block 204.

[0025] In block 204, the processor assesses whether the battery is incondition to execute the exemplary capacitor reform procedure. In theexemplary embodiment, this entails measuring the open-circuit batteryvoltage and determining whether the battery has reached the end of itslife or whether the battery has reached an elective-replacement state.The system deems the battery to have an end-of-life status when the lastrecorded capacitor charge time exceeds a predetermined charge time, suchas 30 seconds, or it has an open-circuit voltage less than 2.1 volts.The system deems the battery to be in an elective-replacement state whenits last recorded charge time exceeds 20 seconds or its open-circuitvoltage is less than or equal to a specific voltage, such as 2.45 volts.If the battery cannot execute the reform procedure, execution of thecapacitor reform procedure is aborted at block 206 to conserve energy.On the other hand, if it can execute reform, execution continues atblock 208.

[0026] In block 208, the processor discharges the capacitors to allow anaccurate measurement of charge time during subsequent procedures. In theexemplary embodiment, the discharge begins on the first cardiac cycleafter initiation of the reform procedure and may require as much as twoseconds to complete. The exemplary embodiment discharges the capacitorsthrough a 1000-ohm load resistor. However, the invention is not limitedto any particular discharge load or rate.

[0027] Block 212 entails charging the capacitors to a high voltage.(Some embodiments include enter a tachy-off mode prior to charging thecapacitors.) The exemplary embodiment charges the capacitors to a highvoltage about 5-15% less than their maximum-energy voltage to avoid orreduce the risk of accelerating aging of the capacitors; however, otherembodiments charge the capacitors to their full rated voltage. Inaddition, charging begins 90-110 milliseconds after the next cardiaccycle and ends when the capacitor voltage reaches the maximum-energyvoltage. (In devices that use blanking intervals, the initiation ofcharging should fall within a blanking interval to reduce the risk offalse arrhythmia detections.) When charging is completed, the exemplaryembodiment records the elapsed charge time in memory.

[0028] In block 214, the processor further charges, or tops off, thecapacitors to maintain the capacitors at a sufficiently high voltage forreform. In the exemplary embodiment implements an N-second top-offprocedure which entails changing the sensed refractory period to 250milliseconds and charging for an M-millisecond period on each cardiaccycle that occurs during the N-second period. N and M are programmableto any desired value; exemplary values for N and M are 5 and 200,respectively.

[0029] In some other embodiments, execution of the top-off procedure iscontingent on whether the measured capacitor voltage is within aspecific voltage range. In one embodiment, this entails determiningwhether the capacitor voltage is greater than the maximum-energy voltageless 10 volts per capacitor in the capacitor system. For example, in aone-capacitor system having a maximum-energy voltage of 185 volts, thisembodiment tops off the capacitor when its voltage falls below 175volts.

[0030] After topping off the capacitors, execution proceeds to block216, to begin an L-second monitoring period. On the first cardiac cycleof this period, the system changes the sensed refractory back to itsnormal (pre-reform) setting, enabling detection of abnormal rhythms. Ifan abnormal rhythm is detected, the system aborts the reform procedureand addresses the abnormal rhythm. The exemplary embodiment sets L to10; however, in general, this value is programmable. If an abnormalheart rhythm or heart condition requiring device therapy is detected,execution branches to block 206 to abort the reform procedure. However,if no condition requiring therapy is detected during the L-secondperiod, execution proceeds to block 218.

[0031] In block 218, the processor determines whether the capacitorshave been at the high voltage for a sufficiently long time period toeffect reform of their tantalum oxide or other reformable portion. Theexemplary embodiment uses a default period in the range of about fiveminutes as a sufficiently long time period. If sufficient time has notelapsed, execution branches back to block 214. Other embodiments useperiods in the range of 15 seconds to 10 minutes. (In conventionaltherapeutic use, capacitors typically hold their charge for a period inthe range of 20 milliseconds to 10 seconds, before initiating atherapeutic discharge.)

[0032] In other embodiments, the sufficient amount of time is based onmeasured electrical properties of the capacitor system. For example, oneembodiment bases the determination on whether the capacitor leakagecurrent has fallen below a certain threshold. To determine a value orproxy for the capacitor leakage current, this embodiment monitors anactual or average time between successive top-offs, with each top-offinitiated when the capacitor voltage falls below a certain voltagelevel. In any event, if the processors determines that a sufficientamount of time has elapsed, the processor executes block 220.

[0033] Block 220 entails initiating or allowing discharge of the one ormore capacitors through a non-therapeutic load. (As used herein,discharge through a non-therapeutic load includes any discharge internalto the device as well as potential discharges at non-therapeutic levelsor rates through the lead system.) The exemplary embodiment dischargesthe one or more capacitors through a 1000-ohm resistor; however, otherembodiments allow the charge to dissipate through system leakage. Stillother embodiments allow the one or more capacitors to float for sometime, for example, 60 seconds, before initiating discharge through aload resistor. Also, one embodiment allows the one or more capacitors todecay through system leakage for a period of time, for example, 60, 90,or 120 seconds or even one or more hours, before initiating dischargethrough a load resistor or other non-therapeutic load. Still otherembodiments, skip or omit blocks 214, 216, and 218 and initiatedischarge of wet-tantalum capacitors through a non-therapeutic loadimmediately upon sensing or otherwise determining that the one or morecapacitors are at the sufficiently high reform voltage. Thus, theinvention is not limited to any particular mode, method, or technique ofnon-therapeutic discharge.

[0034]FIG. 3, which shows an exemplary state flow diagram 300,illustrates an alternate exemplary capacitor-management method embodiedwithin software module 116 and executed by processor 112 and otherrelevant portions of device 100. Diagram 300 includes states or blocks302-322. The exemplary diagram, drawn using commercially availablesimulation software with a state-diagram capability, uses the followingdefinitions:

[0035] CFM_START denotes a request to start the capacitor reformation.The request is made with CFM_TOP_OFF set either true or false, dependingon the number of elapsed days since the last successful capacitorreformation conducted with the top-off of the capacitors to ensureeffective reform.

[0036] CFM_TOP_OFF denotes a parameter set the requester of the reformand determines if the reform will involve use of top off cycles or not.

[0037] SAVE_CHRG, which is normally set to false, controls whether anycharge in the capacitor system is retained to treat a detectedarrhythmia. If an episode results in an abort of the capacitor reform,an abort function sets it true.

[0038] SCHEDULE_CAPFORM, which effects the abort functions, requeststhat a capacitor reform be run again within 24 hours or other specifiedtime. The rescheduled reform will be same type as the aborted reform.For example, if the aborted reform used or was intended to use top off,the rescheduled reform will also use top off.

[0039] CAPFORMTOPOFFDETECTIONTIME denotes the desired value of theDETECTIONTIME when the reform uses top-off. In the exemplary embodiment,this value defaults to five minutes; however, in general, it lies in therange of 15 seconds to 10 minutes or 61 seconds to 10 minutes.

[0040] CAPFORMDETECTIONTIME denotes the desired value of reformconducted without use of top-off. The default value in the exemplaryembodiment is zero.

[0041] CAPFORMTOPOFFINTERVAL denotes the top-off cycle time.

[0042] CHG_ABORT denotes the function of stopping the charging process.

[0043] CHG_DONE is a hardware signal indicating completion of a chargingoperation.

[0044] DETECTION_TIME equals CAPFORMTOPOFFDETECTIONTIME orCAPFORMDETECTIONTIME depending on the value of CFM_TOP_OFF.

[0045] V_EVENT denotes a detection of a ventricular sense, pace orno-sense timeout. However, more generally it denotes a detection of acardiac event.

[0046] SW_CP_DUMP_DONE is a hardware signal denoting completion of acharge dump.

[0047] The exemplary state diagram also makes use of the followingnomenclature: tm=timeout; en=enter; ex=exit. Thus, for example,

[0048] tm(ex(CHARGING), DETECTION_TIME)

[0049] means that when the DETECTION_TIME elapses after exiting theCHARGING state a timeout will occur, triggering the associated path tobe traversed and the state to change.

[0050] The alternate exemplary method begins at idle state block 302.During this state, the processor checks every 24 hours to see if it istime to reform. This entails determining whether it is time to perform ascheduled reform. For example, one can schedule a reform every 90 days.Depending on the value of CFM_TOP_OFF, the reform may or may not involveuse of top offs of the capacitor to maintain capacitor voltage at a highvoltage. Reforms with top off are done every 90 days in someembodiments.

[0051] At state 304, charge in the capacitor system is dumped. Dumpingthe charge facilitates accurate measurement of charging times. Thehardware signal SW_CAP_DUMP_DONE signals completion of the dump andinitiates transition to decision state (or block) 306.

[0052] At block 306, the processor determines if an abort signal or afault, such as a failed dump, has occurred. If so, theRESCHEDULE_CAPFORM function is invoked. If not, a transition to chargingstate 308 occurs. In this state, the capacitors are initially charged totheir maximum-energy voltage. The hardware signal SW_CHARGE_DONEindicates completion of the charging and initiates transition todecision block 310.

[0053] In decision block 310, the processor checks for acharge-time-fault or high-voltage on leads indicating leak. Thecharge-time fault indicates that too much time has elapsed withoutbringing the capacitors to full charge, indicating or suggesting a leakin the system. If there is not fault, a transition to decision block 312occurs. In block 312, the processor checks for an external abort signal.One example of an activity that would result in the external abortsignal is the use of telemetry to reprogram the device.

[0054] A fault at block 310 or an abort signal at block 312 forces atransition to decision block 322. At block 322, the processor decideswhether to save the charge in the capacitors or to dump their charge,based on the value of SAVE_CHRG. With no fault at blocks 310 and 312, atransition to monitor state 313 occurs. Monitor state 313, whichrepresents a parent state, includes three child states: wait state 314,sync state 316, and top-off state 318. The processor essentially staysat monitor state 313 until the reform is completed or aborted.

[0055] More specifically, the transition to monitor state 313 enterswait, or delay, state 314. Wait state 314 waits for a period of time,such as 10 seconds. This time is denoted CAPFORMTOPOFFINTERVAL. Duringthis time, the device essentially looks for arrhythmia episodes. In anepisode occurs, the reform is aborted and rescheduled and there is atransition to decision block 322. If no episode occurs, expiration ofthe time period (CAPFORMTOPOFFINTERVAL) results in a transition to syncstate 316. Sync state 316 waits for the ventricular event, for example,a V-pace, V-sense, or no-sense timeout, before transitioning to top-offstate 318, during which the capacitors are topped off.

[0056] In one version of this alternate implementation, the top offvoltage level is 38 volts less than the voltage for maximum energy for afour-capacitor system. This is to ensure the capacitors are never overcharged. Top off cycles are performed every CAPFORMTOPOFFINTERVALseconds (2-65535 sec) for a duration determined byCAPFORMTOPOFFDETECTIONTIME (0-65535 sec). No top off cycle is allowed tocharge for more than CAPFORMTOPOFFTIMELIMIT (2200-65535 ms). Each topoff charge cycle is started synchronous to a ventricular event to ensurethe charge circuit is activated during a refractory period.

[0057] After the preset DETECTION TIME has expired, there is atransition from monitor state 313 to decision block 320. Decision block320 transitions to dump block 304 to dump the charge on the if noarrhythmia episode is in progress.

CONCLUSION

[0058] In furtherance of the art, the inventors have not only discoveredthe need to reform wet-tantalum capacitors in implantable medicaldevices, but also devised suitable reform methods and software. Theexemplary method conducts reform every 90 days regardless of interveningtherapeutic events, with reform entailing holding one or morewet-tantalum capacitors at a high voltage (within 10 percent of therated capacitor voltage) for about five minutes. Other embodimentsreform hybrid capacitors in medical devices generally and holdhigh-voltage charges on capacitors for times greater than one minute.Other applications for the invention include non-medical devices thatrequire or would benefit from long-term stability of the chargingefficiency of wet-tantalum capacitors.

[0059] The embodiments described above are intended only to illustrateand teach one or more ways of practicing or implementing the presentinvention, not to restrict its breadth or scope. The actual scope of theinvention, which embraces all ways of practicing or implementing theteachings of the invention, is defined only by the following claims andtheir equivalents.

What is claimed is:
 1. A capacitor-reform method comprising: charging atleast one wet-tantalum capacitor in an implantable medical device;allowing the one wet-tantalum capacitors to discharge through systemleakage after charging the one wet-tantalum capacitor in the implantablemedical device; and discharging the one or more of the wet-tantalumcapacitors through a non-therapeutic load, after allowing the one ormore wet-tantalum capacitors to discharge through system leakage.
 2. Themethod of claim 1, wherein the implantable medical device has a housingand the non-therapeutic load is a resistor within the housing.
 3. Themethod of claim 1, wherein the one wet-tantalum capacitor comprises atantalum anode and a non-tantalum cathode.
 4. The method of claim 1,wherein the implantable device includes means for defibrillation, meansfor cardioversion, or means for pacemaking.
 5. A capacitor-reform methodcomprising: charging at least one wet-tantalum capacitor to a highvoltage relative its rated voltage or maximum-energy voltage; partiallydischarging the one the wet-tantalum capacitors through system leakageafter charging the one wet-tantalum capacitor to the high voltage; anddischarging the one or more of the wet-tantalum capacitors through anon-therapeutic load, after partially discharging the one or morewet-tantalum capacitors through system leakage.
 6. The method of claim5, wherein the high voltage is about 90 percent of the rated voltage ora maximum-energy voltage for the capacitor.
 7. The method of claim 5,wherein the implantable medical device has a housing and thenon-therapeutic load is a resistor within the housing.
 8. The method ofclaim 5, wherein the one wet-tantalum capacitor comprises a tantalumanode and a non-tantalum cathode.
 9. The method of claim 5, wherein thepartial discharging is initiated after a time period of at least 60seconds.
 10. The method of claim 5, wherein the implantable deviceincludes means for defibrillation, means for cardioversion, or means forpacemaking.
 11. A capacitor-reform method comprising: charging at leastone wet-tantalum capacitor in an implantable medical device, in responseto a reform signal from a processor in the medical device; allowing theone wet-tantalum capacitors to discharge through system leakage aftercharging the one wet-tantalum capacitor in the implantable medicaldevice; and discharging the one or more of the wet-tantalum capacitorsthrough a non-therapeutic load, after allowing the one or morewet-tantalum capacitors to discharge through system leakage.
 12. Themethod of claim 11, wherein the implantable medical device has a housingand the non-therapeutic load is a resistor within the housing.
 13. Themethod of claim 11, wherein the one wet-tantalum capacitor comprises atantalum anode and a non-tantalum cathode.
 14. The method of claim 11,wherein the implantable device includes means for defibrillation, meansfor cardioversion, or means for pacemaking.
 15. A capacitor-reformmethod comprising: charging at least one wet-tantalum capacitor in adevice to a voltage; allowing the one wet-tantalum capacitors todischarge through system leakage after charging the one wet-tantalumcapacitor in the device; and discharging the one or more of thewet-tantalum capacitors through a load, after allowing the one or morewet-tantalum capacitors to discharge through system leakage.
 16. Themethod of claim 15, wherein the device has a housing and the load is aresistor within the housing.
 17. The method of claim 15, wherein the onewet-tantalum capacitor comprises a tantalum anode and a non-tantalumcathode.
 18. The method of claim 15, wherein the device is implantableand includes a housing and at least one of means for defibrillation,means for cardioversion, and means for pacemaking; and wherein the loadincludes a resistor within the housing.